Method of cleaning an electrostatographic imaging surface

ABSTRACT

An electrostatographic imaging system wherein the imaging surface is cyclically cleaned of residual nonaqueous liquid developer by contacting the imaging surface with a cleaning liquid which is miscible with the nonaqueous liquid developer to dissolve substantially all residual liquid developer. Removal of the miscible cleaning liquid and dissolved liquid developer from the imaging surface may be accomplished with a thin film of liquid being permitted to remain on the imaging surface for every cycle.

United States Patent 1191 Komp 1 Jan. 28, 1975 METHOD OF CLEANING AN3,129,115 4/1964 Clark, etal. 118/637 3,186,838 6/1965 Graff, et al.355/15 X ELECTEOSTATOGRAPHIC IMAGING 3,227,549 l/ 1966 Ullrich, et alll8/DIG. 23 SURFA E 3,501,294 3/1970 Joseph 96/1.5 x [75] Inventor;Richard J, Komp, Bowling Green, 3,697,263 10/1972 Mammino 355/15 X K3,748,127 7/1973 Amidon et al. 117/37 LE X [73] Assignee: XeroxCorporation, Rochester, NY. OTHER PUBLICATIONS 5 Hider; T. M., IBMTechnical disclosure Bulletin, Vol. [22] 1972 9, N0. 11, April, 1967, p.1528. [21] Appl. No.: 280,635

Primary Examiner-Robert L. Lindsay, Jr. Related Apphcamm Data AssistantExaminer-Marc L. Caroff [62] Division of Ser. No. 886,634, Dec. 19,1969, Pat. No.

3325959 [57 ABSTRACT 52 us. c1. 355/15, 15/1035, 96/1 LY,electrostatosraphic imaging System wherein the 7 37 LE, 11 37 x 34imaging surface is cyclically cleaned of residual non- 511 1111. c1.603g 13/14, G03g 13/22 aq"eous liquid developer by contacting theimaging 58 Field 61 Search 134/6, 9; 117/37 LE; Surface with a cleaningliquid which is miscible with 118/D]G 23 55 5; 15/100 1035-, thenonaqueous liquid developer to dissolve substan- 9 1 LY, 1'4 tially allresidual liquid developer. Removal of the miscible cleaning liquid anddissolved liquid developer [56] References Cited from the imagingsurface may be accomplished with a UNITED STATES PATENTS thin film ofliquid being permitted to remain on the if f 1 3,084,043 4/1963 Gundlach96/] LY lmagmg Su ace every Cyc 3,128,683 4/1964 Rubin 117/37 LE X 8clfllms, 1 Drawing Flgllre METHOD OF CLEANING AN ELECTROSTATOGRAPHICIMAGING SURFACE This is a division of application Ser. No. 886,634,filed Dec. 19, 1969, now U.s. Pat. No. 3,725,059.

BACKGROUND OF THE INVENTION This invention relates to imaging systems,and more particularly, to improved cleaning systems and techniques.

The formation'and development of images on the surface ofphotoconductive materials by electrostatic means is well known. Thebasic electrostatographic process, as taught by C. F. Carlson in U.S.Pat. No. 2,297,691 involves placing a uniform electrostatic charge on aphotoconductive insulating layer, exposing the layer to alight-and-shadow image to dissipate the charge on the areas of the layerexposed to the light and developing the resulting electrostatic latentimage by depositing on the image a finely divided electroscopic materialreferred to in the art as toner. The toner will normally be attracted tothose areas of the layer which I retain a charge, thereby forming atoner image corresponding to the electrostatic latent image. This powderimage may then be transferred to a support surface such as paper. Thetransferred image may subsequently be permanently affixed to a supportsurface as by heat. Instead of latent image formation by uniformlycharging the photoconductive layer and then exposing the layer to alight-and-shadow image, one may form the latent image directly bycharging the layer in image configuration. The powder image may be fixedto the photoconductive layer if elimination of the powder image transferstep is desired. Other suitable fixing means such as solvent orovercoating treatment may be substituted for the foregoing heat fixingstep.

Similar methods are known for applying the electroscopic particles tothe electrostatic latent image to be developed. Included within thisgroup are the cascade development technique disclosed by E. N. Wise inU.S. Pat. No. 2,618,552; the powder cloud technique disclosed by C. F.Carlson in U.S. Pat. No. 2,221,776 and the magnetic brush processdisclosed, for example, in U.S. Pat. No. 2,874,063.

Development of an electrostatic latent image may also be achieved withliquid rather than dry developer materials. In conventional liquiddevelopment, more commonly referred to as electrophoretic development,an insulating liquid vehicle having finely divided solid materialdispersedtherein contacts the imaging surface in both charged anduncharged areas. Under the influence of the electric field associatedwith the charged image pattern, the suspended particles migrate towardthe charged portions of the imaging surface separating out of theinsulating liquid. This electrophoretic migration of charged particlesresults in the deposition of the charged particles on the imagingsurface in image configuration.

A further technique for developing electrostatic latent images is theliquid development process disclosed by R. W. Gundlach in U.S. Pat. No.3,084,043 hereinafter referred to as polar liquid development. In thismethod, an electrostatic latent image is developed or made visible bypresenting to the imaging surface a liquid developer on the surface of adeveloper dispensing member having a plurality of raised portions orlands defining a substantially regular patterned surface and a pluralityof portions depressed below the raised portions or valleys. Thedepressed portions of the developer dispensing member contain a layer ofconductive liquid developer which is maintained out of contact with theelectrostatographic imaging surface. Development is achieved by movingthe developer dispensing member loaded with liquid developer in thedepressed portions into developing configuration with the imagingsurface. The liquid developer is believed to be attracted from thedepressed portions of the applicator surface in the charged field orimage areas only. The developer liquid may be pigmented or dyed. Thedevelopment system disclosed in US. Pat. No. 3,084,043 differs fromelectrophoretic development systems where substantial contact betweenthe liquid developer and both the charged and uncharged area of anelectro-. static latent image bearing surface occurs. Unlikeelectrophoretic development systems, substantial contact between thepolar liquid and the areas of the electrostatic latent image bearingsurface not to be developed is prevented in the polar liquid developmenttechnique. Reduced contact between a liquid developer and the nonimageareas of the surface to be developed is desirable because the formationof background deposits is therebyinhibited. Another characteristic whichdistinquishes the polar liquid development technique fromelectrophoretic development is the fact that the liquid phase of a polardeveloper actually takes part in the development of a surface. Theliquid phase in electrophoretic developers functions only as a carriermedium for developer particles.

In copending application of Alan B. Amidon, Joseph Mammino, and RobertM. Ferguson, Ser. No. 839,801 filed July I, 1969, now abandoned,entitled Imaging Systems an imaging technique is disclosed wherein anvelectrostatic latent image is developed by placing the imaging surfaceadjacent a patterned applicator surface having a substantially uniformdistribution of raised portions or lands and depressed portions orvalleys" and containing a relatively nonconductive liquid developer inthe depressed portions of the applicator. Liquid developers having aconductivity of from about 10 to about 10 (ohms-cm) are surprisinglyattracted to the image portions without any substantial electrophoreticparticle separation of particles from the liquid.

While 'capable of producing satisfactory images this development systemcan be improved upon in certain areas. Particular areas of improvementinclude development systems employing a reusable or cycling imagingsurface. In these systems, for example, a photoconductor such as aselenium or a selenium alloy drum as the photoconductor surface ischarged, exposed to a light and shadow image and developed by bringingthe image bearing surface into developing configuration with anapplicator containing developing quantities of liquid developer thereon.The liquid developer is transferred to the imaging surface in imageconfiguration. Thereafter the developer pattern on the imaging surfaceis transferred to copy paper where the liquid developer may be absorbedby the paper to form a permanent print. During the transfer operationnot all of the liquid developer is transferred to the copy paper and asubstantial quantity may remain on the imaging surface. In order torecycle the imaging surface this developer must be eitherremoved orimmobilized, otherwise it will tend to be present as background insubsequent cycles. lf the liquid developer is relatively conductivehaving a resistivity less than about ohm-cm any residue remaining on theimaging surface may damage charge acceptance of the imaging surface bylaterally dissipating electrostatic charge subsequently put on it. Thislateral conductivity of residual liquid developer may lead todegradation of image resolution. While lateral conductivity is ofsecondary importance in development systems employing the more resistiveliquid developers the problem of progressive accumulation of liquiddeveloper on the imaging surface in each cycle still persists. Thisprogressive accumulation of developer residue results in an overall lossof density, deterioration of fine detail and contributes to increasedbackground deposits onthe final copy, particularly since accurateimaging on the imaging surface may be inhibited.

Procedures to remove the residual developer liquid from the imagingsurfaceafter each cycle have been employed. However, to provide thenecessary removal of residual liquid developer the cleaning step must beso severe and complete that there may be a progressive degradation ofthe imaging surface lessening the useful life span. The severity of thecleaning step is dictated by the fact that in cleaning a liquid filmfrom a surface the film is progressively split so that on each separatecleaning about one half the liquid remains on the imaging surface. Insome instances and with complete removal of the residual developer theelectrical properties of a photoconductor, for example, may be virtuallydestroyed by the cleaning operation after only a small number of cycles.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide a developing system which overcomes the above noteddeficiencies.

It is another object of this invention to provide a novel cleaningsystem.

It is another object of this invention to provide a cleaning systemwhich makes more efficient use of cleaning materials.

It is another object of this invention to provide a simple cleaningsystem capable of cyclical use.

It is another object of this invention to provide a liquid developmentsystem superior to known systems.

.It is another object of this invention to provide a cleaning systemsuperior to known systems. I

The above objects and others are accomplished generally speaking byproviding a cycling electrostatographic imaging system having a cleaningsystem which enables cleaning of residual liquid developer withoutdegradation of the imaging surface. More specifically, residualnonaqueous liquid developer remaining on an electrostatographic imagingsurface after the developer has been transferred to a receiver sheet inimage configuration is-cyclically cleaned by contacting the nonaqueousresidual developer on the imaging surface with a cleaning liquid whichis miscible with the nonaqueous liquid developer. The cleaning liquid isemployed in an amount sufficient to dilute and disperse within itsubstantially all of the residual liquid developer. In a liquiddevelopment system employing a cycling or reusable electrostatographicimaging surface and also employing a fairly resistive nonaqueous,non-water compatible liquid developer, the residual developer remainingon the imaging surface in any one cycle is cleaned from the surface bydirectly contacting the imaging surface with a fibrous materialmoistened with a cleaning liquid and then removing the excess liquidincluding dispersed pigment by contacting the imaging surface with a dryfibrous material. By so applying the cleaning liquid to the imagingsurface the residual liquid developer is effectively dissolved andparticulate material, such as pigment, is suspended within the cleaningliquid and removed from the imaging surface. While it is highlydesirable to provide an electrostatographic imaging surface which iscompletely free of residual liquid developer in a development systememploying an aqueous liquid developer it is surprisingly found that inthe development technique of this invention employing a nonaqueous,fairly resistive liquid developer that a thin film principally ofcleaning liquid and containing minor quantities of liquid developer maybe permitted to remain on the imaging surface for each cycle.

The invention may be further illustrated by reference to the FIGURE ofthe accompanying drawing in which an electrostatic latent image isplaced on the imaging surface illustrated as a rotating cylindrical drumphotoconductor 10 such as a selenium drum by uniformly placing apositive charge on the drum by charging means 11 and then exposing thecharged surface to a light-and-shadow image through exposure means 12.The electrostatic latent image is developed at developing station 13 andthe developer on .the imaging surface in image configuration istransferred to a receiver sheet such as ordinary paper 14 which is movedthrough the transfer zone in contact with the drum at the same rate andin the same direction as the periphery of the drum. The paper to whichthe developed image is transferred is held in transfer position byidlers 15. The residual developer present on the electrostatographicimaging member is cleaned from the imaging member at a cleaning station.At the cleaning station a porous absorbent roll 24 is rotating in a bath23 of a cleaning liquid and is in contact with one side of an absorbentfibrous cleaning web 17. The cleaning web 17 is slowly advanced fromsupply reel 19 through idlers 21 and 22 into wiping contact with theimaging surface and finally into takeup reel 18. The cleaning web ispreferably moved slowly in the direction countercurrent to the directionof the advancing imaging surface so that the cleanest portion of the webcontacts the cleanest portion of the imaging surface. In any imagingcycle, during the initial stages of contact between the cleaning web andimaging surface the cleaning liquid and the residual liquid developerare intimately mixed together with large or gross quantities of liquidbeing absorbed by the cleaning web. As a result of the counter currentmotion of the imaging surface and the cleaning web the residual liquiddeveloper and the cleaning liquid are removed from the imaging surfaceby the cleanest portion of the cleaning web. The cleaning liquidapplicator roller 24 supplies cleaning liquid to the absorbent cleaningweb 17 and the cleaning liquid passes through the cleaning web andcontacts the imaging surface and there dilutes and disperses the liquiddeveloper in the cleaning liquid. This countercurrent movement ofimagingrsurface and cleaning web provides in the order of sequence inwhich they take place on the imaging surface the removal of grossquantities of cleaning liquid and liquid developer together with theloosening of residual developer on the imaging surface; the uniformdistribution of cleaning liquid over the imaging surface to providedissolution of liquid developer vehicle and suspension of particulatematerial in the cleaning liquid; and the absorbent removal of residualmixture of cleaning liquid, liquid developer and substantially allparticulate material in web 17 The cleaning liquid applicator roller 24may be independently driven or driven by contact with the absorbentfibrous material and may be retractable from the web surface to providecleaning liquid only on demand. It may also be desirable in certainmachine configurations to provide a cleaning system which is retractablyengagable with the imaging surface.

It is also contemplated that additional configurations of cleaningliquid applicator, absorbent fibrous mate rial, or web configurationsmay be employed. For example, the configurations disclosed in copendingapplication of R. Komp and R. M. Ferguson, Ser. No. 886,633 entitledImaging System and filed concurrently herewith, now abandoned, may beemployed.

The cleaning technique according to the instant invention has been foundto be particularly effective in cleaning nonaqueous liquid developersfrom electrostatographic imaging surfaces. By nonaqueous development ornonaqueous developers it is intended to define that group of liquiddevelopers which are not water compatible and can therefore be describedgenerally as oil based materials having dielectric constants less thanabout 3.5 and surface tensions less than about 40 dynes/cm. These liquiddevelopers are relatively electrically nonconductive and are based onvehicles having a bulk resistivity greater than about ohm-cm. Anysuitable developer from this class may be employed. Typical vehicleswithin this group that may be employed singly or in combination includemineral oil, vegetable oils such as castor oil, peanut oil, coconut oil,sunflower seed oil, corn oil, rapeseed oil, and sesame seed oil. Alsoincluded are hydrocarbon oils, fluorocarbon oils such as DuPonts Freonsolvents and Krytox oils, silicone oils, kerosene, carbon tetrachloride,octane, toluene, oleic acid, and drying oils such as linseed and tungoil. In addition, as is well known in the art, the developers maycontain one or more secondary vehicles, dispersants, pigments or dyes,viscosity controlling agents, drying oils or additives which contributetofixing the pigment on the copy paper. In the development techniquesdescribed in U.S. Pat. application Ser. No. 839,801, the preferred andmost practical operating range of resistivity providing balance betweenconducsidual developer and cleaning liquid. To facilitate comtivity,time constant for lateral discharge and develop:

ment speed is from about 2 X 10 to about 10 ohm/cm.

Any suitable cleaning liquid which is miscible with the liquid developermay beemployed. Typical cleaning liquids include the nonaqueous,non-water compatible liquids discussed above and any additional liquidswhich are miscible with aparticular developer employed and have a bulkresistivity greater than about 10 ohm/cm. Typically, thecleaning-liquids have dielectric constants and surface tensions in theranges stated with respect to the liquid developers. Typical materialsinclude hydrocarbon oils, coconut oil, vegetable oils, such as peanutoil, sunflower seed oil, rapeseed oil, corn oil, fluorocarbon oils,silicone oils, carbon tetrachloride, toluene and oleic acid. Thecleaning liquid should be so selected that they do not have adeleterious effect on either the imaging surface which they are to cleanor on any of the materials or machine components with which they come incontact and particularly should not chemically attack the absorbentfibrous material which applies the cleaning liquid to the imagingsurface. Additionally, the cleaning liquids are preferably nonodorousand nontoxic and have flash points in excess of ll0F.

A particular advantage of the development system according to thisinvention is that the residual liquid developer and cleaning liquid neednot be completely removed from the imaging surface on each imagingcycle. Instead the wiping contact or cleaning of residual liquiddeveloper and cleaning liquid on the imaging surface may be sufficientonly to leave a thin film on the imaging surface. With incompletecleaning, however, it is preferred to provide a substantially continuousthin film of residual liquid developer and cleaning liquid on theimaging surface in order to provide uniformity on the imaging surface.The thickness of any film remaining on the imaging surface must,however, be closely controlled in order to avoid any problems of imagingthrough a thick layer of liquid or dissipation of charge on the imagingsurface. In order to provide adequate imaging capability it is preferredto provide a thin layer which is substantially transparent so thatimaging may take place through this layer of liquid. Typically, the

film of residual liquid developer and cleaning liquid on the imagingsurface may be present in the layer up to a thickness of about 1 micron.lfa layer much in excess of 1 micron in thickness is provided itwill betoo thick to provide adequate definition and resolution of imagecharacters and may contribute to undesirable background. The latitude inmechanical operation which permits the presence of a thin layer ofresidual liquid developer and cleaningliquid on the imaging surfaceaccording to the technique of this invention is highly desirable fromthe automated machine point ofuview since rigorous cleaning operations,materials and techniques are not required.

Where optimum image resolution and contrast are desired it is generallyperferred to provide an imaging I surface which has been cleaned ofsubstantially. all replete removal of the imaging surface it ispreferred to provide a cleaning liquid which is readily evaporated orremoved from the imaging surface. Preferably a cleaning liquid which hasa medium range volatility or will evaporate at a temperature'below atemperature which may thermally degrade any of the other materials andin particular the imaging surface is employed. When employing a materialof medium or high range volatility a simple heating lamp may be employedto provide adequate vaporization of the cleaning liquid. Any residualcleaning liquid containing non-aqueous developer dissolved thereinremaining on the imaging surface may, however, be removed with the useof a highly absorbent porous material.

The cleaning liquid may be applied to the imaging surface in anysuitable manner. Typically, an absorbent porous material containingabsorbed cleaning liquid may be employed. Particularly effectiveapplication of cleaning liquid is obtained with highly absorbent fi'brous and porous materials. Theporous materials may be employed inthe'configu'rationof a sponge. The absorbent fibrous materialslm ay beemployed in the configuration of felt tips; brushes or wicks. Theypreferably are in the form of continuous webs to facilitate the rapid,continuing -'re supply of new cleaning and applicating surfaces and toprovide both applicating and removal surfaces. Since the fibrousmaterial may function as a liquid cleaning applicator to the imagingsurface and may also function as an absorbent sheet, thefibrous'material should have sufficient wet strength that it does notrip or part when it is wetby the cleaning liq- "uid. The fibrousmaterial is preferably softer than the imaging member so as to notabrade it, is lint free so as not to offset lint or other particulatematter to the imaging surface and is not chemically reactive with eitherthe liquid developer or the imaging surface. The fibrous may be used.Typical fibrous cleaning materials include those made from rayon, nylon,cotton, cheese cloth, flannel, Dacron, polyester fibers, polypropylenefibers, paper and cellulose fibers, combinations of rayon and cotton andmixtures thereof. Particularly satisfactory cleaning is obtained withthose fibrous webs which are substantially homogeneous and thick andhave a high absorbent capacity.

The liquid cleaning material may be supplied to the absorbent fibrousmaterial in any suitable manner. Typical means of supplying the cleaningliquid from a liquid reservoir to the absorbent fibers is by means of anabsorbent, porous wet sponge roll rotating in contact with one side ofthe absorbent web which delivers the cleaning liquid to the imagingsurface on the other side of the absorbent web. Additional means tosupply the cleaning liquid to the absorbent web include dipping theabsorbent web in the cleaning liquid to virtually saturate the absorbentweb. Typical sponge rollers include polyurethane foams and rubbersponges which may be rotating in a bath of cleaning liquid or which maybe fed internally from some cleaning liquid reservoir at a remote site.The cleaning liquid may also be applied to the absorbent fibrousmaterial by means of a porous belt applicator or by means of brushes,capillary tubes, gravure rollers, metallic sponge, unglazed porcelain,or felt tips.

The liquid cleaning material may be supplied to the imaging surface inany suitable amount. Preferably sufficient cleaning liquid is added toassist in loosening residual developer from the imaging surface, inuniformly distributing it over the imaging surface and in removing theparticulate and dissolved colorant. Typically to achieve these results,the cleaning liquid is applied to theimaging surface in an amount offrom about 0.02 to about 1 cubic centimeter per 100 square inches.

in operation an electrostatic latent image is placed on anelectrostatographic imaging surface in conventional manner. The latentimage is thereafter developed with a liquid developer according to anyof the techniques previously discussed. Development preferably isobtained with the use of a patterned surface applicator Y roller whereina liquid developer is present in the depressed portions of theapplicator while the raised portions are substantially free of developerand the developer is pulled from the developer applicator to the imagingsurface in image configuration. After transfer of the developer from theimaging surface to a receiver sheet in image configuration the residualdeveloper is removed from the imaging surface.

The cleaning liquid and residual liquid developer may be removed fromthe imaging surface in any suitable manner. Typically, the imagingsurface maybe wiped with an absorbent material such as a porous spongeor absorbent web. A particularly preferred embodiment in providingeffective cleaning with minimum effort and materials is that illustratedin the FIGURE wherein a cleaning liquid is applied to-an absorbentfibrous web material on one side from a rotating porous sponge rollrotating in a bath of cleaning liquid in an amount sufficient to providea cleaning amount on the opposite side of the absorbent fibrous web.While the cleaning web and the imaging surface may be moved in the samedirection, greatest cleaning efficiency and minimum contact length havebeen found to occur when the web and the plate are moved insubstantially opposite directions. By applying the cleaning liquid tothe absorbent fibrous web at a point during the cleaning contact betweenthe web and the imaging surface intermediate the beginning andterminating cleaning portions, a three section cleaning station isprovided. The imaging surface first encounters a wet section of the websaturated with relatively dirty or developer contaminated cleaningliquid containing dissolved residual liquid developer vehicle anddispersed residual developer solids. The residual liquid developer onthe imaging surface is smeared or distributed over the surface withexcessive quantities of liquid developer being removed. The imagingsurface then passes against progressively cleaner, but still wetsections of the web up to the point of application of initial cleaningliquid and initial formation of cleaning liquid and developer mixture,and finally encounters a dry web which absorbs remaining liquiddeveloper or cleaning liquid. It should be emphasized that the contactbetween the cleaning web when wet and the imaging surface provides thenecessary smearing of cleaningliquid and residual developer to removeresidual developer and cleaning liquid from the imaging surfaceincluding any particles which may have adhered rather tightly to theimaging surface. If necessary or desired, any residual liquid cleaner ordeveloper may be removed by the application of heat. I

Typically, the absorbent fibrous material is in the form of a webpositioned along a portion of the imaging surface. The length of contactbetween the imaging surface and the absorbent fibrous web is dependentupon many factors including, but not limited to, the amount of cleaningliquid necessary to apply, the amount of residual developer necessary toremove the absorbent capacity of the particular fibrous cleaning web thesolvent action of the cleaning fluid and the speed of operation.Typically, with an electrostatographic imaging surface in theconfiguration of a drum the area of contact with the cleaning web maycomprise from about 5% to about 50% of the imaging surface during anyportion of the cleaning cycle. To provide adequate spacing of additionalimaging stations while providing satisfactory cleaning, the cleaning webmay preferably comprise from about 30% to about 40% of the imagingsurface area. While the cleaning and imaging surface may be moved in thesame direction, minimum contact length has been found to occur when theweb and plate are 9. moved in substantially opposite directions. Thecontact length may also be varied to some extent by the application ofpressure between the cleaning web and the imaging surface. However, thepressure must be so regulated so as not to provide any unnecessaryabrading function on the imaging surface. Typically, the pressureapplied between the cleaning web and the imaging surface in both dry andwet portions is between 0.25 and 10 pounds per linear inch of contactbetween the cleaning web and imaging surface. A satisfactory balancebetween minimizing abrasion effects on the imaging surface and absorbingcapacity of the cleaning web is observed with a pressure of from about0.5 to about 10 pounds per linear inchat the line of contact between thecleaning web and the imaging surface. The rate at which a web ofcleaning material is consumed is a function of the rate of platemovement and the relative rate time for adequate absorption of residualdeveloper and cleaning liquid the cleaning web preferably has a speed onthe order of from about 1/100 to about 1/500 of the imaging surfacespeed.

Any suitable electrostatographic imaging surface may be cleaned with thetechnique of this invention. Basically any surface upon which anelectrostatic charge pattern may be cyclically formed or developed maybe employed. Typical electrostatographic imaging surfaces includedielectric materials, dielectrics coated on conductive surfaces such asplastic coated papers or metal belts, xeroprinting masters,electrographic recording surfaces, photoconductors and overcoatedphotoconductors. Typical photoconductors that may be employed includeselenium and selenium alloys, cadmium sulfide, cadmium sulfo selenide,phthalocyanine binder coatings and polyvinyl carbazole sensitized with2,4,7 trinitrofluorenone. The electrostatographic imaging surface may beemployed in any suitable structure including plates, belts or drums andmay be employed in the form of a binder layer. For more effectivecleaning, it is preferred to provide a surface to be cleaned which has avery smooth surface and generally the more smooth and uniform thesurface the better will be the cleaning.

" When a recycling or reusable photoconductor is employed as theelectrostatographic imaging surface in the development systems accordingto this invention, it may be desirable to add a small amount of anappropriate Lewis acid or base to the cleaning liquid. Unless anappropriate Lewis acid or base has been provided as a constituent of theliquid developer according to the technique described by J. Mammino andA. Amidon in application Ser. No. 838,328 entitled Imaging Systems andfiled July 1, 1969, it is preferred to provide a small amount of thisadditive inthe cleaning liquid. The addition of an appropriate Lewisacid or base enables the photoconductors to maintain their ability toaccept and hold charge for every imaging cycle. The mechanism by whichthis is accomplished, however, is not fully understood at the currenttime. However, by providing a small amount of an appropriate Lewis acidand Lewis base, the electrical properties of reusable photoconductorsmay be cyclically rejuvenated and imaging quality through successiveimaging steps maintained. For any particular photoconductor, theadditive to the cleaning liquid is specially selected between the twogroups of materials, Lewis acids and Lewis bases. Gen erally, forphotoconductors which are positively charged, Lewis bases are employedand for photoconductors which are negatively charged, Lewis acids areemployed. Typical examples of Lewis bases include among others, thetriarylmethane dyes'such as crystal violet, malachite green,pararosaniline, basic fuchsin; xanthane dyes such as rhodamine B, eosin,erythrosine and fluorescein; aniline dyes such as nigrosine and anilineblack, solid soluble porphyrin derivatives such as tetraphenyl porphineand copper chlorophyllin; thionine dyes, such as methylene blue andthionine; amines such as triphenylamine, polycyclic aromatic andheterocyclic compounds such as anthracene, pyrene, fluorene, acridene,carbazole and their basic derivatives, aromatic hydroquinones, diaminophenyl oxazoles and triazin. Typical Lewis acids include among others,indanthrone dyes, such as anthrazol blue lBC, azo dyes such as naptholblue black, B, benzoazurin G; aromatic compounds such as 2,4,7trinitrofluorenone, tetrachlorophthalic anhydride, chloranil, fluoranil,anthraquinone, and 2-dicyanomethylene-l,3-indanedione. The Lewis basenigrosine is a particularly preferred material in obtaining optimumrejuvenation of electrical properties for positively charged selenium orselenium alloy photoconductor.

The appropriate Lewis acid or base should be present at least in anamount necessary to maintain the electrical properties of a cyclingphotoconductor. They may be insoluble or soluble in the cleaning liquid.For better cycling characteristics it is preferred that they at least bemolecularly dispersed in the liquid in order to insure completeavailability to the entire photoconductor surface and to insure maximumrejuvenation and stabilization of the photoconductor. To provide maximumstabilization of the photoconductor, the Lewis acid or base preferablyis at least partially soluble in the cleaning liquid. Typically theLewis acid or base is present in an amount of from about 0.1% to about0.5% by weight of the cleaning liquid.

DESCRIPTION OF PREFERRED EMBODIMENTS The following preferred examplesfurther define and describe the preferred materials, methods andtechniques of the present invention. Example II is presented forcomparison purposes. In the examples all parts and percentages are byweight unless otherwise specified.

EXAMPLE I An imaging system similar in configuration to that depicted inthe FIGURE is assembled. A photoconductor in the form of a drum having adiameter of about 8 inches comprising a surface layer of selenium ofabout 20 microns thick on a conductive aluminum substrate is positivelycharged to about 450 volts and exposed to a light-and-shadow image inconventional manner. The electrostatic latent image is developed bymoving a patterned surface applicator roll having developing quantitiesof developer in depressed portions thereof past the image bearingsurface so that liquid developer is pulled out of the depressed portionsto the image bearing surface in image configuration. The developmentspeed is about 12 inches per second. The

developer employed is of the following-composition by weight:

Drakeol 9 48 parts Microlith CT Black 33 parts Ganex V216 19 partsDrakeol 9 is amineral oil with a kinematic viscosity of about 17centistokesat 38 C. and a specific gravity of about 0.839-to 0.854 at 25C. available from Pennsylvania Refining Company. Microlith CT Black is aresinated predispersed carbon black pigment available from ClBA: GanexV216 is an alkylated polyvinyl pyrrolidone available from GAF. Thedeveloper on the photoconductor is transferred to bond paper in imageconfiguration. A cleaning liquid applicator comprising a polyurethanefoam wrapped on a steel core to provide a roll about 1 2% inches indiameter is independently driven in contact with a bath of Sohiovolt 35,a hydrocarbon liquid sold by Standard Oil of Ohio, on the one side andin contact with a fibrous absorbent web on the other side. The web ismade of cotton fibers dispersed in a Nylon binder sold by ChicopeeMills, Incorporated as type 3427. The cleaning liquid applicator spongeis positioned at the 6 oclock position with respect to the drum andabout midway between two idler rollers which position the cleaning webin contact with the selenium drum along about 30% of its area. Thecleaning vweb is advanced in the direction opposite to the selenium drumat a speed of about l/450th that of the drums speed. The first printobtained with this appara- .tus is free of background, has image densityof 0.95, a

background of 0.01 and resolution of about 5 line pairs per millimeter.The selenium drum has a substantially continuous film of cleaning liquidon its surface in a thickness of about 0.5 microns. After repeatedcycling of 40 prints, no significant change of print quality isobserved.

EXAMPLE u tion dropping to about 2 lp/mm after about 6 cycles.

while the background increases.

EXAMPLE III An overcoated photoconductor about 9 inches by 14 inches indimension comprising a one quarter mill film of polyethyleneterephthalate obtained from E. l. du- Pont de Nemours and Company underthe trade name Mylar overcoated on a 20 micron thick layer of seleniumon a flat aluminum substrate prepared according to the procedure. ofExample I in U.S. Pat. No. 3,251,686 is charged and exposed to alight-andshadow image in conventional manner. The electrostatic latentimage is developed in the manner described in Example I with a developerof the following composition by weight:

' Flexricin P6 50 parts Ganex V2l6 20 parts Isopar H Cottonseed oilparts 5 parts Isopar H is a synthetically prepared paraffinichydrocarbon liquid having a specific gravity of 0.76 and a viscosity at25 of 1.30 centipoises available from Humble Oil and Refining Company.The wet web is advanced against the overcoated photoconductor under apressure of about 0.3 pounds per linear inch. Thereafter, the overcoatedphotoconductor is contacted with a substantially dry cleaning web of anonwoven rayon fabric sold by Chicopee Mills, Incorporated under thename of Masslinn Fabric type S-1000. The first print obtained with thistechnique has a clean background and image density of 1.0 and aresolution of about 9 line pairs per millimeter. On repeated cyclingafter 55 prints, the quality is observed to remain the same.

EXAMPLE IV Five parts of the liquid developer of Example I are dilutedwith 95 parts of mineral spirits to provide an electrophoretic liquiddeveloper. An electrostatic latent image is formed on a clean seleniumxerographic plate comprising a surface layer of selenium about 50microns thick on a conductive aluminum plate in conventional manner. Theselenium plate is uniformly contacted with the liquid developer byimmersing the plate in a bath of developer. The pigment particles in thedeveloper migrate to form an image on the selenium plate. The developeradhering to the photoconductor is transferred to bond paper in imageconfiguration. A cleaning fabric as described in Example 1 saturatedwith mineral oil (Drakeol 9) is moved across the plate under a pressureof about 0.5 pound per linear inch. The first print obtained is free ofbackground and has an image density of 1.2 and a resolution of about 35line pairs per millimeter. The cleaned selenium plate has a residualfilm ofless than 1 micron of substantially clear mineral oil on itssurface. The above procedure is repeated for an additional 50 cycles. Nosignificant change in print quality is observed.

The technique of this invention provides a sufficient cleaning of anelectrostatographic imaging surface such that imaging may be cyclicallyaccomplished in the presence of a thin film of liquid developer orcleaning liquid on the imaging surface. The cleaning technique has theadvantage of providing a very fast and efficient manner of cyclicallyproviding an imaging surface without any significant abrasion ordegradation of the imaging surface and in a manner that requires veryfew mechanically moving parts. It further provides a cleaning systemwhich minimizes contamination of mechanical movements or the excessiveuse of liquids and conserves expendable material by applying onlysufficient cleaning materials, cleaning liquid, and cleaning web to thearea to be cleaned.

Although specific materials and operational tech niques are set forth inthe above exemplary embodiment using the cleaning technique of thisinvention,

these are merely intended as illustrations of the present invention.There are other materials and techniques than those listed above whichmay be substituted with similar results. Other modifications of the'present invention will occur to those skilled in the art upon a readingof the present disclosure which modifications are intended to beincluded within the scope of this invention.

What is claimed is:

l. A method of cleaning nonaqueous liquid developer from anelectrostatographic imaging surface comprising contacting said surfacewith a cleaning liquid miscible with said liquid developer by l. placingsaid imaging surface in wiping contact with an absorbent fibrousmaterial which makes continuous contact across the width of said imagingsurface of from -50 percent of the area of said imaging surface,

- 2. applying said cleaning liquid across the full width of said fibrousmaterial at a point intermediate the limit of contact of fibrousmaterial and said imaging surface, and

3. providing counter movement between said imaging surface and saidfibrous material, so as to provide a cleaning progression ranging from afirst region of fibrous material saturated with a comparatively highconcentration of residual liquid developer in said cleaning liquid, anintermediate region of fibrous material saturated with a comparativelylower concentration of residual liquid developer in said cleaning liquidand a last region of dry fibrous material adapted to leave, aftercleaning, a substantially continuous transparent film of cleaning liquiddiluted-residual developer on said imaging surface.

2. The method of claim 1 wherein said film is less than about 1 micronin thickness.

3. The method of claim 1 wherein said fibrous material comprises a webin contact with the imaging surface and wherein the miscible cleaningliquid is supplied to the opposite side of said cleaning web by contactwith a liquid reservoir.

4. The method of claim 1 wherein said imaging member is a reusablephotoconductor.

5. The method of claim 4 wherein the photoconductor is selected from thegroup consisting of selenium and selenium alloys.

6. The method of claim 4 wherein said cleaning liquid contains a smallamount of a material selected from the group consisting of Lewis acidsand Lewis bases.

7. The method of claim 1 wherein said contact is contact under pressureof from about 0.25 to about 10 pounds/linear inch.

8. The method of claim 1 wherein the liquid vehicle of said nonaqueousliquid developer has a conductivity less than 10 ohm/cm.

1. A METHOD OF CLEANING NONAQUEOUS LIQUID DEVELOPER FROM ANELECTROSTATOGRAPHIC IMAGING SURFACE COMPRISING CONTACTING SAID SURFACEWITH A CLEANING LIQUID MISCIBLE WITH SAID LIQUID DEVELOPER BY
 1. PLACINGSAID IMAGING SURFACE IN WIPING CONTACT WITH AN ABSORBENT FIBROUSMATERIAL WHICH MAKES CONTINUOUS CONTACT ACROSS THE WIDTH OF SAID IMAGINGSURFACE OF FROM 5-50 PERCENT OF THE AREA OF SAID IMAGING SURFACE, 2.APPLYING SAID CLEANING LIQUID ACROSS THE FULL WIDTH OF SAID FIBROUSMATERIAL AT A POINT INTERMEDIATE THE LIMIT OF CONTACT OF FIBROUSMATERIAL AND SAID IMAGING SURFACE, AND
 2. The method of claim 1 whereinsaid film is less than about 1 micron in thickness.
 2. applying saidcleaning liquid across the full width of said fibrous material at apoint intermediate the limit of contact of fibrous material and saidimaging surface, and
 3. PROVIDING COUNTER MOVEMENT BETWEEN SAID IMAGINGSURFACE AND SAID FIBROUS MATERIAL, SO AS TO PROVIDE A CLEANINGPROGRESSION RANGING FROM A FIRST REGION OF FIBROUS MATERIAL SATURATEDWITH A COMPARATIVELY HIGH CONCENTRATION OF RESIDUAL LIQUID DEVELOPER INSAID CLEANING LIQUID, AN INTERMEDIATE REGION OF FIBROUS MATERIALSATURATED WITH A COMPARATIVELY LOWER CONCENTRATION OF RESIDUAL LIQUIDDEVELOPER IN SAID CLEANING LIQUID AND A LAST REGION OF DRY FIBROUSMATERIAL ADAPTED TO LEAVE, AFTER CLEANING, A SUBSTANTIALLY CONTINUOUSTRANSPARENT FILM OF CLEANING LIQUID DILUTED-RESIDUAL DEVELOPER ON SAIDIMAGING SURFACE.
 3. providing counter movement between said imagingsurface and said fibrous material, so as to provide a cleaningprogression ranging from a first region of fibrous material saturatedwith a comparatively high concentration of residual liquid developer insaid cleaning liquid, an intermediate region of fibrous materialsaturated with a comparatively lower concentration of residual liquiddeveloper in said cleaning liquid and a last region of dry fibrousmaterial adapted to leave, after cleaning, a substantially continuoustransparent film of cleaning liquid diluted-residual developer on saidimaging surface.
 3. The method of claim 1 wherein said fibrous materialcomprises a web in contact with the imaging surface and wherein themiscible cleaning liquid is supplied to the opposite side of saidcleaning web by contact with a liquid reservoir.
 4. The method of claim1 wherein said imaging member is a reusable photoconductor.
 5. Themethod of claim 4 wherein the photoconductor is selected from the groupconsisting of selenium and selenium alloys.
 6. The method of claim 4wherein said cleaning liquid contains a small amount of a materialselected from the group consisting of Lewis acids and Lewis bases. 7.The method of claim 1 wherein said contact is contact under pressure offrom about 0.25 to about 10 pounds/linear inch.
 8. The method of claim 1wherein the liquid vehicle of said nonaqueous liquid developer has aconductivity less than 10 10 ohm/cm 1.